Using Computer Serial Port to Realize AC Servo Motor Control

In the automatic control system, the role of the AC servo motor is to convert the signal (control voltage or phase) into mechanical displacement, that is, to change the received electrical signal to a certain speed or angular position of the motor. He has high accuracy and low frequency characteristics. With the characteristics of high rated speed and short response time, it has been more and more widely used in automatic control systems.

If the microcomputer is used to control the AC servo motor, more methods are used to select the existing motion control card. The microcomputer communicates with the interface board supporting the control card to realize the control of the motor. This control is simple and reliable, but in some occasions where the linkage of the axes of the system is not demanding, the ready-made control card is slightly wasted (control card). The price is around RMB 10,000. Here is a control method. He can control the servo motor at a lower cost. = System Block Diagram As shown in Figure 2 The first task that the serial communication system must implement is the serial communication between the microcomputer and the computer. In the DOS environment, to achieve serial communication between the microcontroller and the computer, as long as the computer chip interface with the communication chip 8250 port address operation. However, in the Windows environment, due to the independence of the system hardware, the user is no longer allowed to directly operate the serial port address. If the user wants to perform serial communication, the API API function of Windows can be called, but due to its high degree of specialization, Therefore, the use of more complex. Microsoft's Visual Basic provides a communication control (Mscomm), using it to easily solve this problem. The new generation of object-oriented programming language VisualBasic is a wonderful combination of Windows programming environment and basic language programming simplicity. He is concise and easy to use, practical, and therefore has been widely 6.0 should provide a communication control named MSCOMM32.OCX, he has the basic serial communication capabilities: that is, through the serial port to transmit and receive data for applications The serial communication function can be added to form FORM from VB TOOLBOX. If there is no such control in TOOLBOX, Shell IJ uses PROPORT's COMPONENT to add him from Windows's SYSTEM directory to VB 6.0's TOOLBOX. This allows you to freely set his properties and communicate with the serial port using Visual Basic statements. The MSComm control has a number of important properties. The main ones are: Settings to set and return the baud rate, parity, data bits, and stop in substrings. BitPortOpen sets and returns the status of the communication port as well as opening and closing the port.

Input returns and deletes characters from the receive buffer.

Output writes a string to the transmit buffer.

With this control, communication between the upper and lower units can be easily implemented.

3 control circuit in the control circuit in order to achieve high-precision servo control, the position feedback device must have 4 times the frequency to improve the code disk resolution, the output pulse and then by the reversible counter to count up and down, the computer in each sample In the cycle, the value of the reversible counter is first read as the actual movement position of the coordinate axis, and then compared with the desired position command of the coordinate axis sent by the difference compensation program, the current coordinate axis speed command voltage is calculated, and the position control = this control is present. Many disadvantages mainly include position control circuit using many components, complex circuits, debugging is difficult, reliability is not very high, and the phenomenon of pulse loss is easy to occur; the control algorithms are all completed by computer software, the sampling frequency is low, and multi-axis control is difficult Compared with this, the use of LM628 dedicated control chip will play a multiplier effect of the company's production of motion control chip, he has a 32-bit position, speed, acceleration registers; programmable digital PID controller with 16-bit parameters, PID control of position error; two working modes: speed and position; he Real-time reading of the set and actual motion parameters (position velocity acceleration); trapezoidal wave velocity curve can be generated automatically, making the acceleration and deceleration stable and the code disc pulse is automatically multiplied by 4; programmable differential sampling interval; support 8-bit Or 12-bit DAC data output; 8-bit parallel asynchronous host interface; host interrupts that can be programmed in real time. LM628 provides 23 self-instructions, including speed setting, acceleration setting, stop motion, setting PID parameters, etc. These instructions are used to simplify the development process of software and hardware. The control process is as follows. Take the three-axis control circuit as an example, 89C52 is based on The instruction requires the selected movement axis through 74LS138, sends the data to 74LS245 74LS245 and sends the data to the LM628's two-way data input/output port. After the LM628 processes the command, the digital signal of the voltage signal is sent to the AD767 through the DAC output port; finally The AD767 converts the digital quantity to an analog voltage to control the motor speed. 4 Software development In order to make this control system versatile, it can be applied to the control of other three-axis AC servomotors in the future, and a method for developing a control library function is used. As shown in the block diagram, it corresponds to the interface on the control circuit, and the basic functions provided by the LM628 are refined such as setting speed, setting acceleration, and emergency stop. In this way, only the library functions need to be transferred to enable programming. .

In the upper computer software system design, first establish a basic module Basic.bas, which is the library function mentioned above. He contains the basic structure of the motion control and control software. For the convenience of programming, build a specific module, Specific.bas, and Basic. The functions in the bas module are further refined, and the commands are concreteized to make them specific modules of this system. Specific, bas is a class module developed on the basis of Basic.bas using VB object-oriented programming, in which the system software is defined. The required function makes the programming of the upper computer software not need to directly call the abstract function in Basic.bas. For example, it needs to open the servo function that is often used in the system to write: input the character string according to the need and open the corresponding I/O port. If the servo switch is connected to the 5th I/O port, it can be defined as: When the servo needs to be turned on, the OpenServe function can be directly called. This specific function brings great convenience to programming. 5 Communication protocol is to make the upper and lower bits function. Good communication, the establishment of a reasonable and efficient communication protocol is very close to the communication protocol can be master-slave mode, the upper PC is always the master SCM is the passive recipient. Both upper and lower units use data frames to send or receive data in the following frame formats. The PC protocol specifies the following: Each time a PC sends a command, it uses the following procedure: Clears the sending and receiving buffers. - Send command * Waiting + Timeout error A command must be received by the PC before it can receive a response frame. The next time the communication PC sends a status query command to the SCM at intervals of a period between the non-issue command word and the non-wait response, the current system status is displayed. (Continued on page 37) 9 attributes, training identification in three phases, the network learning rate in each phase is 0.2, because the input data has been normalized, and the training initial value is limited to ±2. The recognition rates of the three stages of the neural network at each stage are shown in Table 1. Table 1 Neural network recognition rate at each stage Comparison between the first stage and the second stage Stage 3 Stage 3 Misclassification rate Misclassification rate Noise misjudgment Signal 7% No. T P 4% misjudged as regional S. Teleseismic T misclassified as % Region S signal misjudged as noise 2% Acoustic area S Misclassified as 2 Teleseismic T 2 Region P Region misclassified as % Telecentric Three-phase identification The rates are 9%, 93.%, and 98%. The recognition rate of the signal and noise in the first stage is relatively low. The main reason is that the noise of the seismic signal is more complicated, and the noise is easily misunderstood when the signal to noise ratio is low. Sentence signal.

In the future work, it is proposed to improve the recognition rate by pre-noising the signal. Passing the axis number command to identify the response axis 00: Read command 0: Command failure 1: Command success 11: Interface circuit command command identification area (1 PC machine After sending a command to the MCU, after a certain period of time, the MCU shall return the corresponding response command, and whether the command is normally completed or not is in the last bit of the command identification byte indicates the format of the unified frame, and the response of the single-byte instruction also needs to be included. The length of the data, but the length is 0 6 Conclusion Using the above method can be achieved on the premise of low cost through the computer serial port to the AC servo motor control 1 LM628 motion control chip adoption, reducing the workload of the system hardware and software development The system can be widely applied in the occasions where the requirement for multi-axis linkage is not high, but it also has certain defects, that is, it is difficult to achieve multi-axis linkage, especially when real-time position control of multiple axes is performed, the system cannot competent

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